1. Field of the Invention
The invention relates to a method and a device for guiding steel bands about the longitudinal axis of a continuously working press for the manufacture of particle boards, fiber boards, and plywood boards, which bands transmit the pressing pressure to the material to be pressed and draw the material through the press. More particularly, the invention relates to a method which can be performed on such a device in which the first and second bands are guided, via driving drums and return drums, around a pressing ram and a pressing table, respectively, with the steel bands being supported, with an adjustable pressing gap formed therebetween, on a plurality of co-rotating steel rods which are guided with their axes of rotation extending transversely to the direction of travel of said bands against abutments of the pressing table and pressing ram.
2. Discussion of Related Art
In continuously working presses of this type it is difficult, if not impossible, to align or position the longitudinal axis of the pressing ram and the pressing table so as to be congruent with one another due to the rigid construction of pressing table and pressing ram and the statically fixed arrangement of the pressing table and the pressing ram with respect to one another. An additional disadvantage which is apparent is that the steel bands also deviate from the longitudinal axis for this reason during operation and have to be readjusted.
The practical use of continuously working presses, whether they employ hydrostatic supports or rolling supports having rolling rods, has furthermore shown that with the provision of increasingly long presses in order to achieve greater outputs, it is no longer possible to ensure the necessary control of the steel bands. The limit is a press length of about 28 m. With increasing lengths of up to 40 m and more, slight disruptions occur, for example:
a) disruptions caused by lubricating the steel bands and rolling rods; and
b) disruptions arising in the event of uneven bulk density distribution. These disruptions have a disruptive effect on an on-line control of the press. Consequently, it is not always possible to direct the steel bands back into the center by an angular adjustment of the driving drum axes and return drum axes in accordance with the prior art centering techniques. In the pressing-ram/heated-plate region of the press, and in particular in the first one-third of the high-pressure zone, the steel bands are firmly clamped as in a vise. On adjusting the drum axes over the adjusting path, a somewhat greater elongation results in the intake region than in the clamped region, since the steel band is not clamped in the intake region. The same effect applies to the delivery end. The ratio of the clamped distance in the high-pressure region of the increasingly long presses to the unclamped part thus becomes more and more unfavorable as the press length increases. In order to avoid a one-sided overstretching of the steel bands on adjusting the course of the steel bands, the press must be stopped and all the attendant disadvantages endured.